1. Field of the invention
The present invention relates to a magnetic recording medium, a method of manufacture therefor, and a magnetic read/write apparatus that uses the magnetic recording medium.
2. Description of the Related Art
Recording densities of hard disk device (HDD) as a kind of a magnetic read/write apparatus has recently increased by at least 60% per year, and it is believed that this trend will continue in future. Therefore, magnetic heads and magnetic recording media suitable for high recording density have been developed.
A commercially available magnetic recording medium mounted in the magnetic read/write apparatus is mostly an in-plane magnetic recording medium wherein the axis of easy magnetization in a magnetic film is generally oriented parallel to the substrate. The axis of easy magnetization refers to a direction to which spontaneous magnetization is stably directs, and refers to the direction of the c axis of an hcp structure in the case of a Co alloy.
In the in-plane magnetic recording medium, there is a possibility that the volume per bit of the magnetic film becomes too small when the recording density is increased and magnetic read/write characteristics are deteriorated by thermal fluctuation effects. Also medium noise increases under the influence of a demagnetizing field in the boundary of recording bits when the recording density is increased.
In a so-called perpendicular magnetic recording medium of which the axis of easy magnetization in the magnetic film is generally oriented perpendicular to a substrate, in contrast, recording magnetic domains that have clear boundaries can be formed due to less influence of a demagnetizing field in the boundary of recording bits even when the recording density is increased, and therefore noise can be reduced. Moreover, since the recording density can be increased even if the volume of bits is relatively large, the perpendicular magnetic recording medium has high thermal stability, resulting in much attention being directed to the perpendicular magnetic recording medium. Consequently, a structure of a medium suitable for use in perpendicular magnetic recording has been proposed.
Recently, there has been increasing demand for high-density recording in magnetic recording media. For this reason, it is proposed to use a single pole type head that has high level of writing ability in the perpendicular magnetic film.
To cope with the single pole type head, such a magnetic recording medium has been proposed as a layer made of a soft magnetic material, called a backing layer, provided between a perpendicular magnetic film and a substrate so as to improve the efficiency of the flow of the magnetic flux between the single pole type head and the magnetic recording medium.
As the perpendicular magnetic recording medium, for example, there is widely used a perpendicular magnetic recording medium comprising a backing layer (soft magnetic undercoat film), an orientation control film that enables the axis of easy magnetization of the perpendicular magnetic recording film to orient perpendicularly, a perpendicular magnetic film made of a Co alloy, and a protective film, that are provided on a substrate.
However, even when the backing layer is provided, the magnetic recording medium does not have satisfactory performance in read/write characteristics, and therefore a magnetic recording medium that is better in read/write characteristics has been required.
As a means for improving the read/write characteristics of the magnetic recording medium, it is proposed to use a low noise magnetic material as the perpendicular magnetic film.
Also, some means for improvement are proposed with resect to the structure of the perpendicular magnetic film.
Japanese Patent No. 2669529 proposes to enhance lattice matching properties between a Ti alloy undercoat film and a hexagonal magnetic alloy film and to improve the orientation of the c axis of the hexagonal magnetic alloy film by introducing other elements into the Ti in the Ti alloy undercoat film.
However, when using a Ti alloy undercoat film, exchange coupling in the magnetic alloy film increases and medium noise increases, thereby making it difficult to further increase the recording density.
Japanese Patent Application, First Publication No. Hei 8-180360 proposes to improve the orientation of the c axis of a perpendicular magnetic alloy film by providing an undercoat film comprising Co and Ru between a perpendicular magnetic alloy made of a Co alloy and a substrate.
However, in this magnetic recording medium, the crystal grain diameter of the undercoat film comprising Co and Ru increases. As a result, the magnetic grain diameter in the perpendicular magnetic recording film increases and the medium noise increase, thereby making it difficult to further increase the recording density.
Japanese Patent Application, First Publication No. Sho 63-211117 proposes to provide a carbon-containing undercoat film between a perpendicular magnetic recording film made of a Co alloy and a substrate.
However, when using the carbon-containing undercoat film, the orientation of the c axis of the perpendicular magnetic film deteriorates and the thermal stability deteriorates, thereby making it difficult to further increase the recording density.